Several studies suggest that gastritis, gastric ulcer and stress ulcer result from disruption of the mucosal barrier to H ion. Although a variety of agents have been shown to increase mucosal permeability, little is known about the mechanism(s) which allow the stomach to maintain a high transmural gradient to H ion. Recent studies suggest that salicylate, but not bile salt, increases permeability by altering field strength of the luminal border of isolated gastric mucosa. Sulfhydryl and amino groups of several different membranes of nongastric tissues are important for maintenance of field strength, permeability and active transport processes. This study will examine the effects of sulfhydryl and amino binding agents as well as agents structurally related to salicylate on active and passive cation and anion transport by gastric mucosa in order to determine the significance of field strength or functional significance of amino and sulfhydryl ligands on ion transport. Sulfhydryl and amino reactive agents will be used singly and in combination in the presence and absence of salicylate and bile salt in order to determine the nature of the sites important for the maintenance of permeability and alterations of ion transport. The results will allow determination of mechanisms for maintenance and alterations of mucosal permeability in vitro, which will then be correlated with in vivo studies using sulfhydryl and amino reactive agents. In addition to gaining insight as to the nature of the gastric mucosal barrier, this investigation will also result in a better understanding of the complex interrelationship among ion transport processes in the stomach as well as endocrine and metabolic regulation of ion transport in both fundas and antrum.